My invention relates to an improved binary detecting and threshold circuit, and particularly to such a circuit for detecting a repeated binary word without the necessity for bit synchronization.
In some radio communication systems, it may be desirable or necessary that some transmissions on a particular radio carrier frequency be heard only by a selected receiver or receivers, and that some other transmission on the same particular radio carrier frequency be heard by a different selected receiver or receivers. Such a system has been implemented by means of a continuous tone controlled squelch system, sometimes referred to as CTCSS. However, such systems have required audio tones of frequencies outside and usually below the range of the information or voice frequencies, and such frequencies are difficult to filter. For this reason, some of those systems use binary signals in which a predetermined binary word comprised of a predetermined number and arrangement of binary bits are continuously and repetitively transmitted. In such systems, only the radio receiver or receivers which are programmed to detect the predetermined binary word will be activated so that the transmission is heard.
Accordingly, a primary and general object of my invention is to provide a new and improved binary detecting circuit.
Another and more specific object of my invention is to provide a new and improved binary detecting and threshold circuit for use in radio communication systems.
Another object of my invention is to provide a new and improved binary detecting circuit that can detect binary bits relatively accurately without the necessity of providing synchronization with the desired binary bit time interval.
In such a radio communication system, the signals representing the predetermined binary word are subject to fading and distortion in the radio transmission path. When these signals are demodulated, the binary bits which are reproduced may be inaccurate, so that a decision must be made whether to activate the receiver.
Accordingly, another object of my invention is to provide a new and improved binary detecting circuit for determining the binary significance of bits which may be distorted or deformed during a radio transmission.
Another object of my invention is to provide a new and improved binary signal threshold circuit that permits the threshold to accurately reflect operating conditions in a binary signal radio communication system.